mpt: implement MPT proof Get and Verify

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/core/mpt/proof.go

@@ -0,0 +1,74 @@
+package mpt
+
+import (
+	"bytes"
+
+	"github.com/nspcc-dev/neo-go/pkg/core/storage"
+	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
+	"github.com/nspcc-dev/neo-go/pkg/util"
+)
+
+// GetProof returns a proof that key belongs to t.
+// Proof consist of serialized nodes occuring on path from the root to the leaf of key.
+func (t *Trie) GetProof(key []byte) ([][]byte, error) {
+	var proof [][]byte
+	path := toNibbles(key)
+	r, err := t.getProof(t.root, path, &proof)
+	if err != nil {
+		return proof, err
+	}
+	t.root = r
+	return proof, nil
+}
+
+func (t *Trie) getProof(curr Node, path []byte, proofs *[][]byte) (Node, error) {
+	switch n := curr.(type) {
+	case *LeafNode:
+		if len(path) == 0 {
+			*proofs = append(*proofs, toBytes(n))
+			return n, nil
+		}
+	case *BranchNode:
+		*proofs = append(*proofs, toBytes(n))
+		i, path := splitPath(path)
+		r, err := t.getProof(n.Children[i], path, proofs)
+		if err != nil {
+			return nil, err
+		}
+		n.Children[i] = r
+		return n, nil
+	case *ExtensionNode:
+		if bytes.HasPrefix(path, n.key) {
+			*proofs = append(*proofs, toBytes(n))
+			r, err := t.getProof(n.next, path[len(n.key):], proofs)
+			if err != nil {
+				return nil, err
+			}
+			n.next = r
+			return n, nil
+		}
+	case *HashNode:
+		if !n.IsEmpty() {
+			r, err := t.getFromStore(n.Hash())
+			if err != nil {
+				return nil, err
+			}
+			return t.getProof(r, path, proofs)
+		}
+	}
+	return nil, ErrNotFound
+}
+
+// VerifyProof verifies that path indeed belongs to a MPT with the specified root hash.
+// It also returns value for the key.
+func VerifyProof(rh util.Uint256, key []byte, proofs [][]byte) ([]byte, bool) {
+	path := toNibbles(key)
+	tr := NewTrie(NewHashNode(rh), storage.NewMemCachedStore(storage.NewMemoryStore()))
+	for i := range proofs {
+		h := hash.DoubleSha256(proofs[i])
+		// no errors in Put to memory store
+		_ = tr.Store.Put(makeStorageKey(h[:]), proofs[i])
+	}
+	_, bs, err := tr.getWithPath(tr.root, path)
+	return bs, err == nil
+}

pkg/core/mpt/proof_test.go

@@ -0,0 +1,73 @@
+package mpt
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func newProofTrie(t *testing.T) *Trie {
+	l := NewLeafNode([]byte("somevalue"))
+	e := NewExtensionNode([]byte{0x05, 0x06, 0x07}, l)
+	l2 := NewLeafNode([]byte("invalid"))
+	e2 := NewExtensionNode([]byte{0x05}, NewHashNode(l2.Hash()))
+	b := NewBranchNode()
+	b.Children[4] = NewHashNode(e.Hash())
+	b.Children[5] = e2
+
+	tr := NewTrie(b, newTestStore())
+	require.NoError(t, tr.Put([]byte{0x12, 0x31}, []byte("value1")))
+	require.NoError(t, tr.Put([]byte{0x12, 0x32}, []byte("value2")))
+	tr.putToStore(l)
+	tr.putToStore(e)
+	return tr
+}
+
+func TestTrie_GetProof(t *testing.T) {
+	tr := newProofTrie(t)
+
+	t.Run("MissingKey", func(t *testing.T) {
+		_, err := tr.GetProof([]byte{0x12})
+		require.Error(t, err)
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		_, err := tr.GetProof([]byte{0x12, 0x31})
+		require.NoError(t, err)
+	})
+
+	t.Run("MissingHashNode", func(t *testing.T) {
+		_, err := tr.GetProof([]byte{0x55})
+		require.Error(t, err)
+	})
+}
+
+func TestVerifyProof(t *testing.T) {
+	tr := newProofTrie(t)
+
+	t.Run("Simple", func(t *testing.T) {
+		proof, err := tr.GetProof([]byte{0x12, 0x32})
+		require.NoError(t, err)
+
+		t.Run("Good", func(t *testing.T) {
+			v, ok := VerifyProof(tr.root.Hash(), []byte{0x12, 0x32}, proof)
+			require.True(t, ok)
+			require.Equal(t, []byte("value2"), v)
+		})
+
+		t.Run("Bad", func(t *testing.T) {
+			_, ok := VerifyProof(tr.root.Hash(), []byte{0x12, 0x31}, proof)
+			require.False(t, ok)
+		})
+	})
+
+	t.Run("InsideHash", func(t *testing.T) {
+		key := []byte{0x45, 0x67}
+		proof, err := tr.GetProof(key)
+		require.NoError(t, err)
+
+		v, ok := VerifyProof(tr.root.Hash(), key, proof)
+		require.True(t, ok)
+		require.Equal(t, []byte("somevalue"), v)
+	})
+}